Glass Ionomer Cements Flashcards
what are the types of glass ionomer cements?
conventional GI and resin modified GI
what are the uses of GIC?
restorative, core build up, lining, luting, dressing, fissure sealant, orthodontic cement
what are the two components of GIC?
acid (liquid) and base (glass powder)
what is the acid used in GIC?
polyacrylic acid, with tartaric acid added to control the setting characteristics of the material
which powders are used in GIC?
silica, alumina, calcium fluoride, aluminium fluoride, aluminium phosphate, sodium fluoride
what are anyhydrous materials?
the acid is freeze dried and added to the powder, the liquid is distilled water
what are encapsulated materials?
consistent powder/liquid ratio
what are the 3 phases of the GIC setting reaction?
dissolution, gelation and hardening
what happens in dissolution?
acid goes into solution, H+ ions attack the glass surface, Ca, Al, Na and F ions are released which leaves a silica gel around unreacted glass
what happens in gelation?
initial set is due to calcium ion crosslinking with the polyacid by chelation with the carboxyl groups (calcium ions are bivalent so they can react with two molecules joining them)
what happens in hardening?
trivalent aluminium ions start to crosslink which increases strength, this doesnt start for 30mins and can take a week to complete
what happens if GIC is contaminated after the gelation phase
aluminium ions diffuse from material, excessive drying means water will be lost, saliva contamination causes absorption of water, this all leads to a weak material which will be rough and break
what can be used to protect conventional GIC after placement?
varnishes, resins (DBA), greases/gels (vaseline)
comment on the adhesion of GIC
can bond to enamel and dentine without bonding agent, bond strength not high compared with composite, good sealing ability
what is the bonding mechanism of GIC ?
chelation between carboxyl groups in the cement and Ca on the tooth surface, re-precipitation of calcium phosphate (from hydroxyapatite) and calcium salts from the polyacid onto and into the tooth surface, hydrogen bonding or metallic ion bridging to collagen
what does a good bond require?
clean surface, conditioned surface
what gives materials a better aesthetic presentation?
higher silica content
comment on the mechanical properties of GIC?
poor tensile strength, lower compressive strength than composite, poor wear resistance, lower hardness than composite, higher solubility than composite, good thermal properties, no polymerisation contraction, fluoride release, lower modulus, less susceptible to staining and colour change than composite
how does GIC release fluoride?
they have an initial fluoride release but then they take up environmental fluoride to release when fluoride content in tooth falls
what are the advantages of GIC?
stable chemical bond to enamel and dentine, low microleakage, fluoride release, good thermal properties, no contraction on setting
what are the disadvantages of GIC?
brittle, poor wear resistance, moisture susceptible when first placed, poor aesthetics, poor handling characteristics, susceptible to acid attack and drying out over time, problems bonding to composite
what powder makes up RMGIC?
fluoro-alumino-silicate glass, barium glass, polyacrylic acid, potassium persulphate, ascorbic acid, pigments,
what liquid makes up RMGIC?
HEMA, polyacrylic acid, tartaric acid, water, photoinitiator
what is the dual curing method for RMGIC?
acid base reaction, light activated so free radical methacrylate reaction occurs and resin matrix being formed, acid base reaction continues for several hours, REDOX reaction occurs to ensure deeper parts of material is cured
what is the tri curing method of RMGIC?
acid base reaction, REDOX reaction begins, light activation and free radial methacrylate reaction, continued REDOX reaction after initial mixing, acid base reaction continues within resin matrix for several hours
what are the properties of RMGIC?
good bond to enamel and dentine, superior to conventional GIC, better physical properties, lower solubility, fluoride release, better translucency and aesthetics, better handling
what are the disadvantages of RMGIC?
polymerisation contraction, exothermic setting reaction, swelling due to uptake of water, monomer leaching, reduced strength if not light cured, light curing slows acid base reaction, benzoyl peroxides and bromides released which are cytotoxic, fluoride release no better than conventional GIC
compare RMGIC to GIC
better aesthetics, easier to use, stronger
compare RMGIC to composite resin
easier to use and fluoride release
what are the uses of RMGIC
dressing, fissure sealant, endodontic access cavity temporary filling, luting, orthodontic cement, restoration of deciduous and permanent teeth, base or lining
